I've read half of Ender's Game and half of Ender's Shadow. I always have to re-buy them when going through airport terminals, read a little while waiting for the flight, read a little on the flight, then finally get sleepy and take a nap. Lose the book while on vacation, rinse/repeat. Ditto for the Dresden Files books, I think I've read 1.5 of the 3 I have.
Dale Brown's works are a different story. I can't help but read half the entire book before so much as putting it down for a meal. It helps that I am intimately familiar with the subjects, so I don't have to re-read passages 10 times to make sure I extracted all the meaning from them.
I'd say I usually read about 2 novels a year on average, while traveling.